We the people of the United States,
in order to form a more perfect Union, establish justice, insure domestic
tranquillity, provide for the common defense, promote the general welfare,
and secure the blessings of liberty to ourselves and our posterity, do ordain
and establish this Constitution for the United States of America.

The Preamble describes the purpose of
the government set up by the Constitution. Americans expect their government
to defend justice and liberty and provide peace and safety from foreign
enemies.